Triaryl phosphites



United States Patent 3,492,377 TRIARYL PHOSPHITES Richard H. Kline,Cuyahoga Falls, Ohio, assignor to The Goodyear Tire & Rubber Company,Akron, Ohio, a corporation of Ohio No Drawing. Original application May22, 1961, Ser. No. 111,480, now Patent No. 3,244,661, dated Apr. 5,1966. Divided and this application Feb. 1, 1966, Ser. No.

Int. Cl. C07f 9/12,- C08c 11/66 US. Cl. 260-967 6 Claims Aralkylsubstituted triaryl phosphites which may be used as stabilizer forrubbers.

This is a divisional application of co-pending application Ser. No.111,480, filed May 22, 1961, now U.S. Patent 3,244,661.

This invention relates to a new class of compounds which has been foundto have unusual ability to stabilize rubber. More particularly, it isdirected to a unique class of triaryl phosphites which is useful instabilizing rubber polymers. Various triaryl phosphites have, in thepast, been employed as stabilizers for rubber. However, previously knowncompounds of this class, although reasonably successful stabilizers forrubber polymers, have nevertheless been subject to some rather seriouslimitations. One of the more serious limitations of the previously knownmembers of this class of compounds, for example, triphenyl phosphite andthe alkyl-substituted triaryl phosphites, is their susceptibility tohydrolysis in the presence of water. In the commercial production ofsynthetic rubber stabilizers are ordinarily incorporated into thepolymer while it is in 'an aqueous medium in the form of latex, prior tocoagulation and drying of the fiocculated polymers. Since one of themost important functions of a rubber stabilizer is the protection of theraw polymers during drying and subsequent processing, it will be readilyappreciated that a fundamental requirement of an effective rubberstabilizer is that it must be reasonably stable against hydrolysis andat the same time effectively stabilize the polymer, not only duringprocessing, but during subsequent periods of storage which may in somecases extend for many months.

It is an object of this invention to provide a new class of triarylphosphites that is particularly effective as stabilizers for rubberpolymers. Another object of this invention is to provide a class oftriaryl phosphites that will impart stability to rubber over a longerperiod of time than the previously known triaryl phosphites. A furtherobject of this invention is to provide a class of triaryl phosphitesthat its highly resistant to hydrolysis.

In accordance with the present invention I have found that the foregoingand additional objects can be accomplished by employing as rubberstabilizers triaryl phosphites in which each aromatic ring contains onebenzyl or alpha-methyl-benzyl substituent and wherein the aromatic ringsmay each be further substituted with Patented Jan. 27, 1970 one or morelower alkyl substituents. The compounds of this invention conform to thefollowing structural formula wherein R is a radical selected from thegroup consisting of hydrogen and methyl and wherein R and R" areradicals selected from the group consisting of hydrogen and lower alkylradicals containing from 1 to 5 carbon atoms.

Representative examples of compounds conforming to the above describedformula are:

tri(4-a-methylbenzylphenyl phosphite tri(Z-a-methylbenzyl-4-methylphenylphosphite tri 2-benzyl-4-methylphenyl phosphite tri2methyl-4-n-methylbenzylphenyl phosphite tri3-methyl-6-a-methylbenzylphenyl phosphite tri (2-methyl-4-benzylphenylphosphite tri 3 -methyl-6-benzylphenyl) phosphite tri2,4-dimethyl-6-benzylphenyl phosphite tri 2,5-dimethyl-4-benzylphenylphosphite tri 2-benzyl-4-ethylphenyl) phosphite tri2-benzyl-4-butylphenyl )phosphite tri(2,4-dibutyl-6-a-methylbenzylphenyl phosphite tri(Z-a-methylbenzyl-4-amylphenyl phosphite.

The triaryl phosphite stabilizers of the present invention may be madeby any method known to the art. However, a preferred process forpreparing the symmetrical triaryl phosphites consists of reacting atleast 3 mols of a phenol having a benzyl or alpha-methylbenzylsubstituent and optionally one or more lower alkyl substituents with onemol of a phosphorus trihalide, preferably phosphorus trichloride. Thereaction is carried out under suitable reaction conditions whichnormally include conducting the reaction in an inert atmosphere such asnitrogen. After all of the reactants have been introduced, the reactionis conducted at a reaction temperature that does not substantiallyexceed 200 C. (preferably between and 200 C.) until the evolution ofhydrogen halide is complete.

The following examples are presented as illustrations of the preparationof typical triaryl phosphites of the present invention but they are notto be construed as limiting the scope of the invention.

3 EXAMPLE 1 A charge of 212 grams of Z-a-methylbenzybparacresol wasintroduced into a 50 milliliter reaction flask; 46 grams of PCl wereadded to this charge over a tenminute period. These reactants were mixedat room temperature with nitrogen being introduced below the surface ofthe reactants in order to sweep out HCl gas as it was formed. When allof the PC1 had been added the reaction mixture was heated for one hourat a maximum temperature of 200 C., nitrogen being continuously bubbledthrough the mixture. Volatile materials were then stripped off undervacuum at a pot temperature of 200 C. and millimeters pressure. Atheoretical yield of tri(2-a-methylbenzyl-4-methylphenyl) phosphite wasobtained.

EXAMPLE 2 A mixture of triaryl phosphites was prepared in accordancewith the following procedure: 445.5 grams of a 35/65 mixture of2-benzyl-4-methylphenol and S-methyl- G-benzylphenol were introducedinto a 1-liter flask. The mixture was heated to 70 C. and 102 grams ofPC];, were added slowly over an interval of 40 minutes. The reactionvessel was continuously flushed with nitrogen introduced below thesurface of the reactants to aid in the removal of HCl gas. The mixturewas heated to 200 C. in 30 minutes and maintained at this temperaturefor an additional 90-minute period. Volatile materials were stripped offunder vacuum at 200 C. and -millimeters pressure. A theoretical yield ofa mixture consisting of tri(Z-benzyl-tmethyl-phenyl) phosphite andtri(3- methyl-fi-benzylphenyl)phosphite was obtained.

EXAMPLE 3 A charge of 225 grams of 2-benzyl-4-methylphenol and 52.5grams of PCI;, were introduced into a one-liter reaction flask andreacted under the same experimental conditions as outlined in Example 1.A theoretical yield of tri(2-benzyl-4-methylphenyl)phosphite wasobtained.

EXAMPLE 4 A mixture of triaryl phosphite was prepared by reacting 241.5grams of mono-m-methylbenzyl derivative of USP cresol with 52.5 grams ofPCl following the same experimental conditions as outlined in Example 1.A theoretical yield of a mixture of triaryl phosphites was obtained.

EXAMPLE 5 A charge of 264.5 grams of 2-methyl-4-a-methylbenzylphenol wasintroduced into a one-liter reaction flask. Nitrogen was bubbled throughthe charge which was maintained at 65 C. and 57.5 grams of PC];, wereadded dropwise over a period of ten minutes. The reaction mixture wasthen heated for an additional 90 minutes at a maximum temperature of 200C. with nitrogen bubbling continuously through the reactants. Volatilematerials were removed by heating under vacuum at 200 C. and 12millimeters pressure. A theoretical yield oftri(2-methyl-4-a-methylbenzylphenyl)phosphite was obtained.

Other compounds of this invention were prepared in a manner similar tothe procedure outlined in the preceding examples.

The rubbers which may be conveniently protected by triaryl phosphites inaccordance with this invention are natural rubber and those syntheticoxidizable rubbery polymers of conjugated dienes which are normallysusceptible to deterioration by sunlight and atmospheric oxygen. By theterm oxidizable rubbery polymers of conjugated dienes as employed inthis application, is meant natural rubber and the synthetic rubberypolymers and copolymers of conjugated dienes. Representative examples ofsynthetic oxidizable rubbery polymers of conjugated dienes which arenormally susceptible to deterioration by sunlight and atmospheric oxygeninclude poly chloroprene; polyisoprene having essentially all of itsunits combined in a cis-1,4 structure; polybutadiene having essentiallyall of its units combined in a cis-1,4 structure; the rubbery copolymersof butadiene and styrene which may contain from 50 to or more ofbutadiene; and butyl rubber which is a polymerization product of a majorproportion of a mono olefin and a minor proportion of a multiolefin suchas butadiene or isoprene.

The cis-1,4 polyisoprene rubber mentioned above may conveniently beproduced in accordance with the procedures described in the followingreferences:

(1) Synthetic Natural Rubbers from lsoprene Rubber and Plastic Age, vol.39, No. 11, page 938 (1958) by Mayor, Saltman, and Pierson.

(2) Cis-l,4 Polyisoprene Prepared with Alkyl Aluminum and TitaniumTetrachloride Industrial and Engineering Chemistry, vol. 50, pages1507-1510 (1958) by Adams, Stearns, Smith, and Binder.

The cis-l,4 polybutadiene rubbers mentioned above may conveniently beproduced in accordance with the procedures described in the followingreferences:

(1) New Controlled-Structure Polymer of Butadiene Rubber and PlasticAge, March 1961, pages 276-282 by W. W. Crouch.

(2) 1,4-cis Polybutadiene Gummi und Asbest, vol. 13, page 1026 (1960).

The triaryl phosphite stabilizers of this invention may be used with orwithout other stabilizers, vulcanizing agents, accelerators or othercompounding ingredients. In order to effectively stabilize raw rubber,small proportions of one or more of the triaryl phosphites in accordancewith this invention are added to the rubber polymer in a customaryantioxidant amount which may vary somewhat depending upon the type andrequirements of the rubber articles to be produced. An aqueous oilemulsion of a rubbery butadiene-styrene polymer can be stabilized withfrom 1 to 10 percent of tri(2-a-methylbenzyl-4-methylphenyl)phosphitebased on the weight of the polymer. The triaryl phosphites willgenerally be employed in an amount ranging from 0.25 to 5.0% by weight,based on the weight of the polymer, preferred concentrations generallyrange from 0.5 to 2.0% by weight, based on the weight of the polymer.

The stabilizers of the present invention may be used to stabilize any ofthe above-mentioned rubbers. They are particularly valuable asstabilizers for oil-extended rubbers prepared with any of the well-knownextending oils in accordance with widely practiced commercialprocedures. The triaryl phosphites of the present invention can beconveniently incorporated into rubber by any convenient method such asby adding them to the latex, adding them to a dilute cement prepared bydispersing the rubber in an inert solvent or by milling them into thecoagulated polymer. A preferred method of incorporation consists ofintroducing a small amount of the stabilizer to the latex just prior toor concurrently with the addition of the acid-salt coagulant. It isfrequently desirable to add the stabilizer in the form of an emulsionwhich may be prepared by mixing the triaryl phosphites with water andany of the conventional emulsifying agents such as the fatty acids orsoaps. When the stabilizers of this invention are employed instabilizing oil-extended rubbers they may be conveniently incorporatedin emulsions prepared with a portion or all of the extending oil whichis added to the raw polymers. When the stabilizers of this invention areemployed to stabilize the cis-l,4 polyisoprene or cis-1,4 polybutadienerubbers as described above, a convenient method of incorporationconsists of adding the stabilizers to the inert organic solvent in whichthese polymers are prepared after the polymerization of the monomers isessentially complete.

The triaryl phosphites of this invention were tested as stabilizers forstyrene-butadiene polymers in accordance with the following procedure:

EXAMPLE 6 One and twenty-five hundredths parts of the stabilizers shownin the following table were added to 100 parts of antioxidant-freestyrene-butadiene polymer (SBR-l00 6- a hot styrene-butadiene rubber)which was prepared by the commercial acid-salt coagulation process. Thepolymer was dried in a vacuum oven at a temperature of 50 C. while theoven was flushed with nitrogen. The dried polymer was stored undernitrogen and refrigeration. Portions of the rubber were dissolved inbenzene to form a cement containing approximately 3% rubber and theindicated stabilizers added thereto. The cements were poured ontoaluminum foil so as to form very thin films of rubber when the benzeneevaporated. After drying, the weight of the rubber was obtained inconnection with each sample. Thereafter the foil with the adheringrubber film was placed in the oxygen absorption apparatus. Theoxidation-resistant properties of various triaryl phosphites prepared inaccordance with the present invention were compared with theoxidation-resistant properties of a well-known commercially availabletriaryl phosphite antioxidant. The data obtained are summarized in thefollowing table:

ared by reacting 3 mols of mono benzyl derivative of USP cresol withlmol 01 P01 "A well-known commercially available antioxidant.

EXAMPLE 7 The test procedure outlined in Example 6 above was repeatedusing a second styrene-butadiene polymer (SBR 1508, a coldstyrene-butadiene rubber). One and twenty-five hundredths parts of thestabilizers shown in the following table were added to 100 parts of theantioxidant-free polymer. The remarkable ability of a typical triarylphosphite in accordance with the present invention to protect thisrubber against oxidation is shown by the following data.

TABLE II Hours to absorb Sample N o. Antioxidant 0.5% 0 1.0% 0

1 'Iri(nonylphenyl)phosphite* 86 110 2 Tri(2-a-methylbenzyl-4-methyl-226 366 phenyl)phosphite (Example 1) A well-known commercially availableantioxidant.

EXAMPLE 8 Separate samples of cis-1,4 polyisoprene rubber preparedfollowing a procedure essentially as outlined in the reference by Mayor,Saltman and Pierson cited above, were stabilized against oxidation byincorporating 1.25 parts of the stabilizers shown in the following tableper 100 parts of rubber. The stabilizers were dispersed in the benzenethat was used to dilute the rubber solutions and thus form a cementwhich was then processed and tested in accordance with the procedureoutlined in Example 6.

phosphite and tri(3-methyl-6-benzylphenyl) phosphite (Example 2).

' A well-known commercially available antiodixant.

From the foregoing data it will be apparent that triaryl phosphites ofthe present invention are extremely effective in imparting oxidationresistance to rubber.

The superior resistance of triaryl phosphites of the present inventionto hydrolysis is demonstrated by the following example.

EXAMPLE 9 A weighed sample (about 5 grams) of a triaryl phosphite esteras indicated in the following table was dissolved in 30 milliliters ofisopropyl alcohol and the solution added to milliliters of boilingwater. Ten milliliter aliquots of this solution were removed atintervals and titrated with 0.1 N potassium hydroxide in isopropanolusing bromphenol blue as the indicator. A curve was plotted showing theamount of acid liberated from the ester vs. time. The time for the acidconcentration to reach 50% of its maximum value was taken as a measureof the hydrolytic stability of the triaryl phosphite ester. These valuesfor a number of esters are presented in the following tables. Table IVshows the results obtained when a few drops of HCl were added to theester prior to hydrolysis. Table V shows the data obtained from neutralsystems.

Table IV Minutes to 50% Compound: hydrolysis Tri(nonylphenyl)phosphite*22 Tri(2. benzyl 4 methylphenyl)phosphite 43 Tri(4 a methylbenzyl 4methylphenyl) phosphite 43 Tri(2 a methylbenzyl 4 methylphenyl)phosphite 47 A mixture of triaryl phosphites prepared by reacting 3 molsof mono-benzyl derivative of USP cresol with 1 mol of PC1 49 A mixtureof triaryl phosphites as prepared in Example 4 64 A mixture of triarylphosphites composed of 45% tri(2-a-methylbenzyl 4 methylphenyl)phosphite and 65% tri(3-methyl-6-a-methylbenzylphenyl)phosphite 82.5

A well-known commercially available antioxidant.

Table V Minutes to 5 0% Compound: hydrolysis Tri(nonylphenyl)phosphite*129 A mixture of triaryl phosphites composed of 35% tri(2-a-methylbenzyl4 methylphenyl) phosphite and 65%tri(3-methyl-6-a-methylbenzylphenyl)phosphite 232 *A well-knowncommercially available antioxidant.

The present invention may be advantageously employed in the manufactureof rubber which is to be used for making a wide variety of articlesincluding tires, tubes, shoes, all types of light-colored rubberarticles, hose, coating compositions, etc.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein 7 without departing from the spirit or scope of the invention.

What I claim is:

1. Triaryl phosphites conforming to the following 20 wherein R and R"are radlcals selected from the group consisting of hydrogen and loweralkyl radicals containing from 1 to 5 carbon atoms.

2. A triaryl phosphite in accordance with claim 1 wherein R and R" arehydrogen.

3. A triaryl phosphite in accordance with claim 1 wherein R and R" aremethyl radicals.

4. A triaryl phosphite in accordance with claim 1 wherein R is a methylradical and R" is hydrogen.

5. The compound tri(2 o: methylbenzy] 4 methylphenyl) phosphite.

6. The compound tri(4-a-methylbenzylphenyl) phosphite.

References Cited UNITED STATES PATENTS 5/1940 Carswell 260967 4/1947Howland et al.

US. Cl. X.R.

qg gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3.592.277 Dated January 27, 1970 Invented!) giggggd H, Kline It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Abatract page 1, line 15, "stabilizer" should road --atab1l1aora- Page3, Example 1, line 3, "50" should read --500--. Page 6, Table IV, lino52, "hSfl'nhould road 35%.

SIGNED NND SEALED JUN 3 0 197!) Fletcher WILLIAM E. scam Mmtins offimComissioner of Patents

